ML20035C227

Discusses BWROG Experiments to Quantify Effects of Noncondensible Gases During Depressurization & to Test Adequacy of Potential Mods.Requests Response to Concerns Stated by 930331

ML20035C227
Person / Time
Issue date:	03/04/1993
From:	Russell W Office of Nuclear Reactor Regulation
To:	Beck G BWR OWNERS GROUP
References
GL-92-04, GL-92-4, NUDOCS 9304060355
Download: ML20035C227 (3)

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March 4, 1993 c

Mr. George J. Beck, Chairman Regulatory Response Group Boiling Water Reactor Owners' Group c/o Southern Nuclear Operating Company P.O. Box 1295, Bin B052 Birmingham, AL 35201

SUBJECT:

BWROG EXPERIMENTS TO QUANTIFY THE EFFECTS OF NONCONDENSIBLE GASES.

DURING DEPRESSURIZATION AND TO TEST THE ADEQUACY OF POTENTIAL MODIFICATIONS In my letter to you on December 2,1992, we accepted a modification to the schedule proposed in Generic Letter No. 92-04 on the basis that the BWROG would be completing experiments in March 1993 that would quantify the effects of noncondensible gases during major depressurization events and would test the adequacy of potential modifications. With the information from these experiments, plant modification plans would be completed by July 1993 and would be implemented at the earliest opportunity.

During a meeting on February 17, 1993, NRC staff observed the initial test setup and discussed with the BWROG the status of the test program..Since that l

meeting, the NRC staff has both general and specific concerns regarding the scope and focus of the testing program, j

i We are particularly concerned that the commitment to test the adequacy of potential modifications will not be fulfilled. At the meeting, testing of r

plant modifications was not mentioned. As previously expressed to you by letter dated December 2,1992 and in our previous meetings, it is the staff's i

I position that modifications must be made and that the staff is skeptical that I

the testing program can demonstrate that no modifications are necessary.

Therefore, you should clarify immediately your plans to test modifications.

Specific concerns with the testing program are provided in the attached enclosure. We continue to expect that these issues will be given priority i

attention. A response to our concerns is requested by March 31, 1993.

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Sincerely, ORIGINAL S!GNED BY W.T. RUSSELL l

William T. Russell, Associate Director 9304060355 930304 for Inspection & Technical Assessment TOPRP EUTO R

Office of Nuclear Reactor Regulation i

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Enclosure:

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j Enclosure'

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i NRC SPECIFIC CONCERNS ON THE BWROG TESTING PROGRAM FOR DEGASSING EFFECTS 1

1.

The BWROG stated that the pipe size to be used during the experiments

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would be one-inch in diameter, and that the resulting data would be j

extrapolated to other piping sizes.

Since reference leg geometries are i

known to exist in smaller sizes, it would appear to be more prudent to j

use piping of a smaller diameter, capturing the effects of the smaller pipe size on potential water ejection from degassing, and extrapolating

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l these data to the larger sizes of piping. We understand that benchtop I

testing will be performed, however, we need more details on this portion l

of the test program.

2.

The BWROG planned to use only one inert gas during the experiments and then to run the data through computer codes to obtain the representative quantities of oxygen and hydrogen generated during degassing events.

The NRC staff strongly recommends the use of a second inert gas for some experiments to correlate the data between the two gases and provide a means to validate the computer codes.

3.

Although the normalization of volume-to-total volume compared with height-to-total height for the test configurations is used to envelope plant-specific piping configurations, the NRC staff remains concerned that the potential degassing holdup effects that may occur within horizontal portions of actual piping configurations are not adequately accounted for in the test configurations. Actual configurations are much more complex than those to be used in the test program. We believe i

that a test examining the multiple horizontal and vertical legs representative of actual plant geometry needs to be performed.

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Temperature effects need to be evaluated during the testing program.

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While temperature may not have a significant effect on the solubility of gases in solution for the pressures of interest, the behavior and 1

effects of those gases once they come out of solution are temperature i

dependent.

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Correlation of the test results needs to consider actual plant-specific data from known degassing events to ensure test results can adequately explain the events.

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